Need help/advice on how to get visitation rights to my niece.?

Its a bit of a sticky situation, but basically my ex-sister in law will no longer let me or any other members of my family see our niece/granddaughter. There was a very small disagreement between me and the sister in law and she hasn't let us see or talk to her for over a year. She was VERY close to everyone in my family and we miss her so much. The only problem is that her dad, my brother, got involved with some bad things a while ago in his life, like drugs, and gave up rights to her. But because of this do the grandparents not have rights still? We are desperately seeking help in this situation. We need any advice or help on where to start. We miss her so much and are ready to do what we can to get her back in our lives. Please any advise or expertise would be greatly appreciated!